The present invention relates to a process and apparatus for the control of a volume of a fluid in a duct system, and more especially to a process and apparatus for controlling the volume of air moving through an air duct system.
Such a process is disclosed in German Offenlegungsschrift No. 2341296. In this known process, as shown by the circuit layout associated therewith, the direct current motor driving the blower is supplied with a constant current, so that the volume of air moved by the blower will increase at a lower rate corresponding to rising dynamic pressures. The volume of air is thus controlled only by means of the motor voltage, i.e., the rpm of the blower, while the blower is constantly exposed to the full dynamic pressure. The disadvantage of this known process is that with rising dynamic pressures the motor voltage may attain the value of zero at a relatively low vehicle velocity, and then the volume of air moving through the blower will be directly proportional to the velocity of the vehicle and of the oncoming flow of air. This condition substantially limits the range of application of this electronic blower control, which in part is no longer suitable for present day vehicles. For the continued functional use of this blower control mechanism, negative motor terminal voltages, in combination with a reversal of the current, would be required even at relatively low vehicle velocities, which would be detrimental for the motor and the circuit of the blower.